【作者】 杨曦凝；

【导师】 梁军；

【作者基本信息】 哈尔滨工业大学 ， 工程力学， 2008， 硕士

【摘要】 超高温陶瓷材料(UHTCs)在国防和航天上发挥着越来越重要的作用,它能够胜任于包括高超声速长时飞行、大气层再入、跨大气层飞行、和火箭推进系统等极端环境,因此它的抗氧化性能是其使用时最重要的参考依据,热化学理论作为一种相对成熟的方法,为研究超高温陶瓷的抗氧化性能提供了一条研究途径。本文利用热化学理论系统的研究了超高温陶瓷的高温氧化机理,探讨了超高温陶瓷高温氧化过程中材料微结构的变化趋势;并利用细观力学理论分析了高温氧化特性对材料力学性能的影响。为了研究超高温陶瓷的高温氧化机理,在1800℃时分别对ZrB2+20vol%SiC(ZS1)、ZrB2+30vol%SiC(ZS2)复合材料进行不同氧分压下的高温氧化实验,并且利用热力学计算软件FactSage进行数值模拟,得出了材料的高温氧化机理;探讨了氧化产物含量对表面形态的影响,与氧化后照片吻合;通过对不同SiC含量和氧分压的材料进行计算,发现SiC含量高对提高材料的抗氧化性能有利,但在低氧分压下由于SiO2的挥发使得这种有利因素不明显;根据氧化产物生成时的氧分压不同,得出了氧化层的示意图,分析出SiC耗散层是影响抗氧化性能的薄弱环节,并与材料测试结果进行了比较分析。在反应物与生成物的总质量守恒以及SiC耗尽层内的固体相体积不变基础上,描述了SiC耗尽层内生成物的体积膨胀以及孔洞的演化随温度的变化规律;把生成相与孔洞视为广义夹杂,通过细观力学的理论预报了SiC耗尽层的高温弹性性能的劣化过程,结果表明,衰减主要受相变的控制,初始SiC含量越高,生成的孔洞体积分数越大,SiC耗尽层的弹性性能衰减也越明显。更多还原

【Abstract】 Ultra high temperature ceramics (UHTCs) is becoming more and more important in national defense and astronavigation region. It can be used in extreme environments including those associated with hypersonic flight, atmospheric re-entry and rocket propulsion. The oxidation resistant properties of UHTCs are the most important reference datum for use. Thermo chemical theory provides a method to study the oxidation-resistant properties as another ripe way.In this thesis, the high temperature oxidation mechanism has been investigated by thermo chemical theory. The change of microstructures after high temperature oxidation has also been investigated. Regarding resultant phases and holes as generalized inclusion, the high temperature oxidation characteristic has been studied by micromechanics method.In order to investigate the high temperature oxidation mechanism, the high temperature oxidation experiments and tests of ZrB2+20vol%SiC(ZS1)、ZrB2+30vol%SiC(ZS2) compositions was done at 1800℃and different oxygen partial pressures ,and the numerical simulation was done by the thermodynamics software FactSage. The high oxidation mechanism was gained. The effects of oxidation resultant content on surface conformation was discussed which is in good agreement with experiment. By calculating compositions at different SiC content and oxygen partial pressures, we found a high SiC content is beneficial for oxidation resistance, but this phenomenon changed with reduced oxygen partial pressure because of the volatilization of SiO2. The proposed oxide layered structure was get with the oxygen partial pressures of the oxidation resultants, and SiC-depleted region is the decisive factor of oxidation resistant properties which was compared with experiment.The expending volume of resultant and the change of holes in SiC-depleted region were described at the base of conservation which includes reactant- resultants conservation and solid phase volume conservation. Regarding resultant phases and holes as generalized inclusion, the bad process of high temperature elasticity property was predicted by micromechanics. It was indicated that attenuation was controlled by phase transformation. The more SiC content at first, the bigger volume fraction with the elasticity property decreased rapidly.更多还原